The invention relates to thermal transfer printing wherein images are formed on a receiving substrate by heating extremely precise areas of a print ribbon with thin film resistors. Heating of the localized area causes transfer of ink or other sensible material from the ribbon onto the receiving substrate. The sensible material is typically a pigment or dye which can be detected visually, optically or magnetically.
In the printing field, the impact type printer has been the predominant apparatus for providing increased throughput of printed information. The impact printers include the dot matrix type wherein individual print wires are driven from a home position to a printing position by individual and separate drivers. The impact printers also include the full character type wherein individual type elements are caused to be driven against a ribbon and record media.
While impact printing has dominated the industry, this type of printing has some disadvantages. One disadvantage of this type of printing is the noise level which is attained during printing operations. Another is that the printing applications are limited to record media which are rigid or can be supported by a platen to resist the impact of the print wires or type elements driven against it during the printing operation.
Thermal printing has been an effective alternative for significantly reducing the noise levels which are attained during printing operations. Since the ink is transferred to the record media by a thermal process, supporting the record media in a rigid fashion is not as critical as in impact printing. Thermal transfer printing has requirements distinct from impact printing which need to be addressed when considering new printing applications. Representative documentation in the area of non-impact printing and thermal transfer printing include the following patents.
U.S. Pat. No. 3,663,278, issued to J. H. Blose et al. on May 16, 1972, which discloses a thermal transfer medium having a coating composition of cellulosic polymer, thermoplastic resin, plasticizer and a xe2x80x9csensiblexe2x80x9d material such as a dye or oxide pigment material.
U.S. Pat. No. 4,315,643, issued to Y. Tokunaga et al. on Feb. 16, 1982, discloses a thermal transfer element comprising a foundation, a color developing layer and a hot melt ink layer. The ink layer includes heat conductive material and a solid wax as a binder material.
U.S. Pat. No. 4,403,224, issued to R. C. Winowski on Sep. 6, 1983, discloses a surface recording layer comprising a resin binder, a pigment dispersed in the binder, and a smudge inhibitor incorporated into and dispersed throughout the surface recording layer, or applied to the surface recording layer as a separate coating.
U.S. Pat. No. 4,463,034, issued to Y. Tokunaga et al. on Jul. 31, 1984, discloses a heat-sensitive magnetic transfer element having a hot melt or a solvent coating.
U.S. Pat. No. 4,523,207, issued to M. W. Lewis et al. on Jun. 11, 1985, discloses a multiple copy thermal record sheet which uses crystal violet lactone and a phenolic resin.
U.S. Pat. No. 4,628,000, issued to S. G. Talvalkar et al. on Dec. 9, 1986, discloses a thermal transfer formulation that includes an adhesive-plasticizer or sucrose benzoate transfer agent and a coloring material or pigment.
U.S. Pat. No. 4,687,701, issued to F. Knirsch et al. on Aug. 18, 1987, discloses a heat sensitive inked element using a blend of thermoplastic resins and waxes.
U.S. Pat. No. 4,698,268, issued to S. Ueyama on Oct. 6, 1987, discloses a heat resistant substrate and a heat-sensitive transferring ink layer. An overcoat layer may be formed on the ink layer.
U.S. Pat. No. 4,707,395, issued to S. Ueyama et al. on Nov. 17, 1987, discloses a substrate, a heat-sensitive releasing layer, a coloring agent, and a heat-sensitive cohesive layer.
U.S. Pat. No. 4,777,079, issued to M. Nagamoto et al. on Oct. 11, 1988, discloses an image transfer type thermosensitive recording medium using themosoftening resins and a coloring agent.
U.S. Pat. No. 4,778,729, issued to A. Mizobuchi on Oct. 18, 1988, discloses a heat transfer sheet comprising a hot melt ink layer on one surface of a film and a filling layer laminated on the ink layer.
U.S. Pat. No. 4,869,941, issued to Ohki on Sep. 26, 1989, discloses an imaged substrate with a protective layer laminated to the imaged surface.
U.S. Pat. No. 4,923,749, issued to Talvalkar on May 8, 1990, discloses a thermal transfer ribbon comprising two layers which remain non-integral. One layer comprises a thermal sensitive coating, the other comprises a protective layer.
U.S. Pat. No. 4,975,332, issued to Shini et al. on Dec. 4, 1990, discloses a thermal transfer ribbon with an adhesive improving layer, an electrically resistant layer and a heat sensitive transfer ink layer.
U.S. Pat. No. 4,983,446, issued to Taniguchi et al. on Jan. 8, 1991, discloses a thermal transfer ribbon comprising a saturated linear polyester resin, a wax and a carbon black pigment.
U.S. Pat. No. 4,988,563, issued to Wehr on Jan. 29, 1991, discloses a thermal transfer ribbon comprising a thermal sensitive coating and a protective coating. The protective coating comprises ethylene vinyl acetate copolymer and wax which provides reduced ribbon offset.
U.S. Pat. No. 5,089,350, issued to Talvalkar et al. on Feb. 18, 1992, discloses a thermal transfer ribbon having a layer comprising a mixture of waxes, a hydrocarbon polymer, an acetate copolymer and fluorescent pigment having a specific color.
U.S. Pat. Nos. 5,128,308 and 5,248,652, issued to Talvalkar each disclose a thermal transfer ribbon containing water-based thermally reactive ingredients for creating colored images. These thermally active ingredients comprise a leuco dye and a phenolic resin which create color upon the application of heat.
And, U.S. Pat. No. 5,240,781, issued to Obatta et al., discloses an ink ribbon for thermal transfer on rough surfaces
To provide printed information on cartons by thermal transfer printing, the information is printed on a label or other medium which is then applied to the carton. The materials and equipment used in preparing and applying the labels comprises a significant portion of the total cost of the printing operation. Printing directly onto the carton would provide significant savings over the use of labels, however, because of limitations on the equipment used and the print obtained, this has not been feasible. The surfaces of cartons are rough and non-receptive to the ink transferred, causing problems in clarity, adhesion, etc. In addition, most conventional thermal transfer printers employ a print head which requires the receiving substrate be fed through a curved or sinusoidal path so that proper handling of the packages would be difficult. Recent advances in print head designs provide an opportunity to overcome this handling limitation; however, problems with the print clarity and adhesion on the rough surfaces still remain.
It is an object of the present invention to eliminate the need for labels in providing thermal printed material on cartons.
It is another object of the present invention to provide a method for printing directly on a carton by thermal transfer printing.
It is yet another object of the present invention to provide a thermal transfer ribbon which allows for the direct application of data onto a carton or package.
Still, another object of the present invention is to provide a thermal transfer ribbon which forms a receptive layer for thermal transfer print.
A further object of the present invention is to provide a thermal transfer ribbon which includes a coating of thermal transfer material that provides a receptive layer for thermal transfer ink and also a coating of thermal transfer ink. Such a ribbon enables the receptive layer and thermal transfer ink to be deposited on a substrate simultaneously.
An additional object of the present invention is to provide a receptive layer for thermal transfer ink which provides a white background for contrast.
These and other objects will be apparent and fully understood from the following description taken together with the annexed drawings and claims.
In a process aspect of the present invention, there is provided a method of printing images directly on a carton. This method comprises printing a receptive layer on the carton by a thermal transfer printer and printing an image on the receptive layer also by a thermal transfer printer. The receptive layer enhances the adhesion of the image to the carton and preferably enhances contrast of the image for scanning purposes.
In a product aspect of the invention, there is provided a thermal transfer ribbon having a flexible substrate and a coating of a thermal transfer material which provides a receptive layer for thermal transfer ink. In certain embodiments, the thermal transfer ribbon additionally contains a coating of thermal transfer ink between the substrate and the coating of thermal transfer material which provides the receptive layer. These embodiments enable simultaneous transfer of the receiving layer and ink layer to a substrate.